In general, requirements for automobile tires are high abrasion resistance, low rolling resistance, low heat build-up, high tear resistance, high groove cracking resistance, high skidding resistance, etc. These properties need to be well balanced. In recent years, the demand for conservation of resources has grown also in the art of tires from the standpoint of environmental protection. Among the foregoing properties, low rolling resistance, which leads to the enhancement of energy efficiency, and high abrasion resistance, high tear resistance and low heat build-up, which prolong the life of tires to enhance the cost performance of materials, are particularly focused. In particular, tires which are used under a large additional load, e.g., tires for truck, commercial car, bus, electric car running with a heavy storage battery on board, etc. are requested to exhibit improvements in the foregoing properties, i.e., low rolling resistance, high abrasion resistance, high tear resistance and low heat build-up while maintaining other general properties. While the automobile is running, the portion of the tire which comes in contact with the ground moves circumferentially and continuously as the tire rotates. During this process, the tread of the tire which has come in contact with the ground undergoes compression deflection, bending deflection and shear deflection under a load while the tread which has been released from the ground restores its original shape. Thus, the various portions of the tire do a repeated work of deflection and restoration. Since the rubber compound constituting the tread exhibits a viscoelasticity in which deflection lags behind stress, it undergoes hysteresis loss during the repeated work of deflection and restoration, converting a part of the driving energy applied to heat energy. This hysteresis loss constitutes the mast part of energy loss accompanying the rolling of the tire called rolling resistance. Thus, the reduction of rolling resistance means nothing but the reduction of the hysteresis loss of the rubber compound constituting the tread. In order to reduce rolling resistance, the formation of the tread by using a rubber compound comprising a rubber polymer which provides a reduced hysteresis loss and carbon black having a large particle size as a reinforcing agent or a reduced amount of carbon black has been attempted. However, the particle size of carbon black relates to its reinforcing effect. Thus, the larger the particle size of carbon black is, the lower abrasion resistance and tear resistance are. Further, when the content of carbon black is reduced, the lowered reinforcing effect is caused, deteriorating abrasion resistance and tear resistance. Therefore, the reduction of rolling resistance without impairing other properties by this method is limited. Accordingly, it is a common practice to form a tread in a 2-layers construction (cap/base). In some detail, the cap, which comes in contact with the ground, is made of a rubber compound having an excellent abrasion resistance while the base, which does not wear in operation, is made of a rubber compound having a low rolling resistance regardless of abrasion resistance. Even in this method, the rolling resistance relates to the sum of the hysteresis loss of the cap and base. If the tread comprises a cap/base construction in which the base is made of a rubber compound having a lower hysteresis loss to exhibit an even lower rolling resistance, the tire undergoes tearing during the terminal period of operation and thus shows a reduced life. Therefore, even such a cap/base construction cannot reduce the rolling resistance to the desired level while maintaining the desired abrasion resistance and tear resistance. From the standpoint of the foregoing problems, JP-A-3-7602 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes a method which comprises the formation of a base by a rubber compound comprising carbon black and silica incorporated therein as reinforcing agents to drastically reduce the rolling resistance of the tire while maintaining endurance of carcass (heat build-up) and tear resistance. Since silica disadvantageously enhances the viscosity of the rubber compound and hence deteriorates the processability thereof as compared with carbon black, it is necessary that the rubber compound having silica incorporated therein comprises a large amount of a softener incorporated therein to have a better processability in order to put itself into practical use. However, if a softener is incorporated in the rubber compound in a large amount, the resulting rubber compound exhibits a reduced abrasion resistance. Therefore, silica is mostly incorporated in the base in the cap/base construction, although the use of silica provides a rubber compound having a low rolling resistance.